how many simultaneous adds?

Question

Right guys - just looking for some experience.

Im looking at a new algorithm thats going to serious eat up my logic with adders (needs a 11x11 matrix of differences summed into single value, and I need as many of these as I can).

Up till now Ive only added 2 values in a single pipeline stage, but can you get away with more? Currently one of these matrix adds is going to take 3% of the registers (5% of LEs) of a EP2AGX125. probably going to look at clocking this at ~150 Mhz, and the 2 inputs per add apparently gives fmax of 390MHz, so Ive got plenty of scope here.

how much does additional adders hurt the Fmax - because I assume I lose the use of the carry chain.

altera_forum · Answer

Take a look at the synthesis cookbook:

http://www.altera.com/literature/manual/stx_cookbook.pdf?gsa_pos=1&wt.oss_r=1&wt.oss=synthesis cookbook

Arria II should be able to do ternary addition without problem. If you do more than that, I don't believe it will break the carry chain, it will just create multiple adders with carry chains feeding each other. Definitely something you're going to have to experiment with to see the breaking point, both from an area and performance perspective.

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how many simultaneous adds?

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